Lipoproteins from plasma and perivelline fluid of the apple snail Pomacea canaliculata.

Structural lipids, primarily phospholipids and sterols, as well as energy-storage lipids such as triacylglycerols are insoluble in water. In the aqueous fluids of animals, they are carried as lipoproteins, complexes of lipids bound to polypeptides. These watersoluble lipoproteins can be separated into different classes, depending upon their hydrated densities. These classes include very low density (VLDL), low density (LDL), high density (HDL) and very high-density (VHDL) lipoproteins. The two first ones predominate in the blood of vertebrates, while HDLs are the main lipoproteins in invertebrate hemolymph. Lipid circulation systems in invertebrates have been studied mainly in the phyla Arthropoda and Mollusca. In terrestrial invertebrates, the mechanisms of lipid circulation are well known in insects and comparatively less known in arachnids. The most studied group of aquatic invertebrates, respect to lipoproteins, is the Crustacea and, in contrast, the phyllum Mollusca has received little attention. In fact, the lipoproteins of only one species of the classes Bivalvia, Cephalopoda and Gastropoda were described up to date. In addition to the lipoproteins common to males and females, there are female-specific lipoproteins, which appear in the hemolymph plasma during vitellogenesis. They are similar to vitellins, the egg lipoproteins that provide energy and nutrient for the developing embryo. These egg storage molecules can also play a role in the growth and survival of larvae. Among aquatic invertebrates, egg lipoproteins have been described in crustaceans, sea urchins and molluscs (for a review, see Lee, 1991). The present review deals with the lipoproteins present in hemolymph and perivitelline fluid of the snail Pomacea canaliculata, their lipid and protein composition, as well as their consumption during the embryo development. This is the only Gastropoda species whose plasma and egg lipoproteins were studied. Results are discussed comparatively with other invertebrates.